In particular, the present invention relates to a test apparatus for testing a circuit unit to be tested having a test system, a control bus for transferring control data from the test system to the circuit unit to be tested, an address bus for transferring addressing data from the test system to the circuit unit to be tested, and a data bus for exchanging test data between the test system and the circuit unit to be tested.
Present-day test systems preferably use an advanced test load (ATE). Test systems of this type make it possible to test electronic circuit units to be tested at a high throughput (throughput numbers) and furthermore to prescribe different parameters such as, for example, different operating voltages for the circuit unit to be tested or different timings of the test data streams.
FIG. 4 shows a conventional test apparatus in which a circuit unit DUT (DUT=Device Under Test) to be tested can be tested by means of a test system. In the schematic block diagram of a conventional test apparatus as shown in FIG. 4, control signals for controlling a test sequence are fed to the circuit unit DUT to be tested via a control bus. Furthermore, specific circuit subunits or memory cells are addressed by means of addressing signals from the test system, the addressing signals being fed via an address bus illustrated.
A data bus is provided between the test system and the circuit unit DUT to be tested in order to exchange test data. Thus, by way of example, desired data are compared, in the test system, with actual data fed from the circuit unit to be tested during a test sequence.
If circuit units to be tested are connected to the test system in a conventional test apparatus, then a ground line for the connection of the ground potential VSS is furthermore present, while an operating voltage line for feeding an operating voltage potential VDD is provided.
Particularly in advanced test apparatuses, it is increasingly of importance to change the operating voltage that is fed during the test, i.e. to prescribe an operating voltage signal in variable fashion. It is disadvantageous that conventional test systems do not enable changes to be made in the operating voltage VDD at an arbitrary point in time. If it is necessary, for example, at an exactly defined point in time, for example after a specific command fed via the control bus, to carry out a voltage change for a specific time, then it is inexpedient that this procedure cannot be carried out by means of conventional test systems. In conventional circuit arrangements, this leads to the essential disadvantage that operating voltage changes such as possibly occur in a subsequent application cannot be simulated by the test system of the test apparatus. Consequently, it is disadvantageous that an extremely low test coverage is achieved in this respect.
In order to carry out changes in the operating voltage VDD, it is necessary, in conventional test systems, to halt a test that is underway, to change the voltage and to continue the test after a transient response. Consequently, operating voltage changes for the circuit unit DUT to be tested can only be carried out in relatively long time periods that cannot be predetermined in variable fashion.